The invention relates to a device for use in a roll frame for the manufacture of a plastics film, having a continuous band, looped around at least two deflection rolls, for pressing the plastics film against a roll of the roll frame and for cooling the same, the two deflection rolls being rotatably mounted on both sides in lateral bearing devices. The invention further relates to a process for changing a continuous band for pressing a plastics film against a roll and for cooling the same, which is looped at least around two deflection rolls rotatably mounted in lateral bearing devices.
In addition to the contact-pressing and cooling of the plastics film, the continuous band, which is generally realized as a continuous metal band, can also be used to transmit the surface of the continuous band to the plastics film.
Such a device is known, far example, from U.S. Pat. No. 6,077,065 and is especially used, in calenders, having two chill rolls, for contact-pressing the plastics film introduced via a nozzle, since relatively thin plastics films with a relatively smooth or structured surface can thereby be manufactured in a simple manner. As alternatives to the continuous band (also referred to as xe2x80x9csleeve bandxe2x80x9d), air knives or even contact-pressing rolls are normally used. Yet the continuous band, especially in respect of plastics films (for example polypropylene films, etc.) with a thickness of between 50 and 500 xcexcm, does have advantages.
Continuous bands of this type, generally consisting of metal, have a relatively short working life, however, and generally have to be exchanged after a few weeks due to wear phenomena, especially cracks in the marginal region. The exchange of the continuous band is complicated, however, since, in known devices, the bearing housings of the roller bearings provided for the rotatable mounting of the deflection rolls have to be opened. Consequently, substantial downtimes are suffered due to the band change.
The object of the present invention is now to create a device of the type stated in the introduction, in which the continuous band can be quickly and easily exchanged and the downtimes of the roll frame are thereby reduced. In addition, a process of the type stated in the introduction is intended to be created for the same purpose.
This object is achieved with the aid of a device of the type stated in the introduction, in which fastening means are provided for fixing the deflection rolls in a bearing device and the other bearing device is pivotably mounted for the exchange of the continuous band. Such a device allows the deflection rolls to thus initially be attached to a bearing device and it is subsequently possible to pivot the other bearing device for the exchange of the continuous band, whilst the deflection rolls are held with freely projecting ends in the other bearing devices. Once the continuous band has been exchanged, the previously pivoted bearing device is swiveled back and the fastening means for fixing the deflection rolls in the other bearing device are re-released. This produces an exchange of the continuous band which is made substantially simpler compared to known devices. Consequently, the downtimes of the roll frame in which such a device is provided are able to be substantially reduced.
If, as the fastening means for fixing the deflection rolls, a fixing ring having a wedge surface is respectively provided, the deflection rolls can be fixed by simple displacement of the fixing rings in the direction of a bearing housing surrounding the bearings of the deflection roll, since a frictional connection is formed between the wedge surface of the fixing ring and the bearing housing of the deflection roll.
To avoid contact, when the bearing device is pivoted, with liquid-carrying lines which are provided, where appropriate, and are connected to the deflection rolls, for example for the chilling thereof, it is favorable if the fixing rings are provided on a side of the device which has ports for a liquid or gaseous medium, especially a cooling medium.
If the bearing device is mounted pivotably about an essentially vertical rotational axis, the bearing device can be laterally pivoted in a simple manner about a, in the fastened position, vertical rotational axis, allowing the continuous band to be exchanged without hindrance. In particular, it is herein favorable if the bearing device is mounted such that it can be pivoted about 90xc2x0, since unhindered access to the deflection rolls fastened in the other bearing device is thereby guaranteed, even where the continuous bands are very wide. The pivoting can also, however, be effected over another range of angle.
A constructively particularly simple design of the pivotable arrangement of a bearing device for the exchange of the continuous band is obtained if, for the pivotable mounting, a centering bolt jutting downwards from the bearing device is provided, which centering bolt is rotatably arranged in a corresponding opening in a receiving plate.
In order to be able to connect the device in modular fashion to a roll frame, it is advantageous if the device is provided on a trolley having a plurality of wheels.
If the pivotable bearing device has conical recesses for receiving conical bearing housings of the deflection rolls, the bearing sleeves of the rolls can easily be inserted into the recesses in the pivotable bearing device and additionally, due to the conical design of both recess and bearing housing, a self-centering of the positive and/or non-positive connection is obtained.
In order to be able to adjust the tension of the continuous band and, in particular, to reduce the tension of the continuous band prior to the band change, it is advantageous if at least one deflection roll is arranged adjustably in the bearing devices. In particular, it is herein advantageous if a pneumatic or hydraulic cylinder is provided for the adjustment of the roll position.
As an alternative thereto, an electric motor with spindle gearing can also be used to adjust the roll position.
For the exact alignment of the continuous band relative to the roll against which the plastics film to be manufactured is pressed, it is favorable if a stand supporting the two bearing devices is arranged such that it is horizontally and vertically adjustable.
At least one of the deflection rolls can be driven by a motor, for example an electric motor.
The process according to the invention, of the type stated in the introduction, is characterized in that the deflection rolls are fixed in a bearing device, fastening means of the other bearing device are released and the other bearing device is pivoted, so that the continuous band can be laterally extracted from the deflection rolls.
Using this process, the time needed to exchange a continuous band due to wear or aging phenomena, just as with the above-described device, is substantially reduced, since there are no split bearing housing shells having to be disassembled.
In order to be able particularly easily to remove the continuous band from the two deflection rolls and insert a new continuous band, it is favorable if the mutual distance between the deflection rolls is shortened before the bearing device is pivoted, since the band tension of the old band is reduced prior to removal and the continuous band does not have to be tensioned for insertion.
If the deflection rolls in the bearing device are respectively fixed by means of a fixing ring having a wedge surface, the deflection rolls can easily be rigidly fastened in a bearing device, by bracing of the wedge surfaces between the roll and the bearing housings surrounding the roll, and at the same time centered.
For a simple, easily manageable pivoting of the bearing device, which, in a pivoted position, allows unhindered access to the two fixed deflection rolls, it is advantageous if the bearing device is pivoted about an axis disposed essentially perpendicular to a receiving plate. In particular, for an unhindered change of continuous band, it is herein advantageous if the bearing device is pivoted about 90xc2x0.